Fuel container



Aug'. 26, Q46.

FUEL CONTAINER Filed.A Jan. 22, 19.42

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INVENTQR.

DfJ.. SULL-IVAN 2,405,986

Patented Aug. 20, 1946 UNITED STATES PATENT oFF-ica FUEL CONTAINER'.

David. J.. Sullivan, Fairfield, Conn., assignor to E. I. du Pontde Nemours & Company, WilmingtonDe1., a corporationA of Delaware ApplicationJanuary'ZZ, 1942, Serial No. 427,838

4 Claims. 1.

This invention. relates to fuel. containers and more particularly toI an improved. fuel container of the self-sealing type.

The fuel containers or cells. which. this invention is designed to improve are those composed of a plurality of. layers of. material and in which it is desired that the layer in Contact with: the fuel be completely impermeable thereto and Wholly resistant to` its solvent action. More particularly this invention is concerned with the improvement of self-sealing containers of the. kind subjectto machine gun nre-as for example those used on military aircraft, combat. vehicles such as tanks, armored-cars, etc. These: fuel-cells, for example, may comprise a layer of solvent.` resistance neoprene', or like synthetic rubber, in contact with the fuelcontents, a. layer, such as neoprene compoundedwith softeners, which expands mechanically to close perforations, a layer such as raw rubber'which swells. rapidly to close l the perforation when the initially escapingi liquid contacts this layer, and an outer covering of vulcanized rubber, leather, etc.

In the variations in. such constructions: and materials used therein, it is desirable; in the interests of long life inthe cell that thev synthetic rubber layer be provided. with aflexible coa-ting which is impervious to the fuel and insensitive to its solvent action, inasmuchas theV first. mentioned synthetic rubber layer, which has been previously used as the; inner liner has. been found to permit some diffusionv of. fuel vapor and tof increase in weight undesirably onv continued contact With the .fuel and is particularly' subjectto attack by aromatic hydrocarbon fuels. If thezfuel seeps into the next layer' of softened synthetic rubber, or particularly if it` entersv the: raw rubber layer, the cell deteriorates. rapidly; i'. e. its sealing properties are adversely affectedv and the cell wall may be distorted.

In the` application ofy Harold S. Holt, Serial No. 427,837, filed of even date herewith, there is dis'- closed 1a fuel cell in which the inner liner is. applied as a sheeting composed of a polyamide' of the rubbery type, particularly the polyesteramides. These. polymers can be applied. as relatively thick sheets because, being rubbery as are the other laminaethe flexibility of the cell', which is a characteristic desirable in aircraft. use, is. not impaired. The use of. thin films of. these poly'- mers ist not practicable because their fabrication into thin sheets requires excessive milling which degrades thesheet.. and because those lms that can be obtained from solution inthe case.- of the 2. rubbery polymers. are not sufficiently impermeable to the. hydrocarbon fuels.

In the case. of, the above mentioned rubbery polyester-amides,various difficulties are encountered when it is attempted, as in the practice of this invention, to use films of such thinness as will retain, the required'. flexibility in the tank rather than to use thicker films Which, sincethey are rubbery like the remaining laminae, do not impair the ilexibility ofthe cell. vrIhese dif'culties, in addition to that of impermeability previously mentioned, include that of adhesion which has been avoided previously by the. use of intermediate brous material,V Such as Wood flour, to permit the use of specific cements for the different laminae. For these. and other reasons the full advantages inherent in the application of the thin films thatfcan be obtained from solutioncannot be realized in the absence of the further requirements described. herein.

This invention has as an. object an improved fuel container. A. further object is a fuel cell or container composed. of a plurality of' laminae inv which. the inner lines. is a ilexible thinv iilm or skinA of highly impervious substance bonded to a supporting layer of rubbery material. Other objects will appear hereinafter.

The abovev objects are accomplished by applying as the inner .liner of a. flexible fuel tank `a thin film. of synthetic linear polyamide in accordanceswiththe procedure which will be more fully described. In one aspect of.` my invention improvedv fuel cells of the type previously described are. obtained by means ofl an inner liner consisting of al thin', flexible, solvent impervious polyamide film or skin directly and strongly bonded to the rubbery layer bycertain resins. In another aspect of the invention the cells are improved by applying with the above. mentioned or other suitable bonding means` a thinfilm. of a polyamide described in more detail below which I have found tof be peculiarly adapted to the present-purpose.

The polyamides used in. the practice of' this invention. are of the general type. described in U. S. Patents 2,071,253 and 2,130,948. The polyamides of this kind are the reaction products of linear polyamide-forming ccmpositions, for example onel composed of bifunctional reacting materialY containing two amide-forming groups each of whichv is complementary to` an amide- ,forming group in other molecules in said composition. Ihese polyamides as describedv above yor as. otherwise identified hereinafter canv be ob.- tained, for.l example, by self-polymerization of a monoaminomonocarboxylic acid, or by reacting a diamine with a dibasic carboxylic acid in substantially equimolecular amounts, it being understood that reference herein to the amino acids, diamines and dibasic carboxylic acids is intended to include the equivalent amide-forming derivatives of these reactants. In the polymers made with these reactants the average number of carbon atoms separating the amide groups is at least two. On hydrolysis with hydrochloric acid the amino acid polymers yield the amino acid hydrochloride and the diamine-dibasic acid polymers yield the diamine hydrochloride and the dibasic carboxylic acid.

In the accompanying drawing Fig. 1 is a perspective view of a fuel bodying the invention, and

Fig. 2 is a sectional view through one of the walls illustrating a preferred construction.

The fuel tank l, the top, bottom, side and end walls of which are fabricated as shown in Fig. 2, can be of any desired shape and is provided with an outlet 5 leading to the fuel line not shown. The outlet 5 can consist of a metal tube or a neoprene or a polyamide lined rubber tube provided with a flange 6 which is cemented or vulcanized to one of the laminae comprising the cell. A similar flange 6, having a fuel inlet consisting of an upright portion 3 providing with a cap 2 is cemented or otherwise Secured to the cell.

The numeral 'l indicates the inner layer of thin impermeable and solvent resistant synthetic linear polyamide which in use is in contact with the fuel contents and which is bonded by means of the resin adhesive 8 described below to the layer 9 of fully polymerized neoprene or other synthetic rubber or rubbery material. The substances of this kind disclosed herein are tough, water-insoluble materials having substantial resistance to the fuel contents which are usually aliphatic and/or aromatic hydrocarbons. The numeral l0 designates a layer of material (for example neoprene compounded with softeners and having a softness of 30 durometer as compared to the harder layer 9 of 60 durometer) which mechanically expands or stretches under the deforming action of the puncturing object and then by its resilience returns to its original position, thus closing the puncture to reduce the leakage of fuel to a minimum. A layer of raw rubber l l or other material which swells readily on contact with the fuel is provided as a means for stopping or further reducing any leakage not completely stopped by the layer I0. The layer l2 is a protective covering which may be composed of leather, vulcanized rubber or other suitable flexible material. The layers 9, l0 and Il are adhered by suitable cements or mutual solventsin accordance to well known procedure.

The material shown in Fig. 2, in which the size of the layers have been .exaggerated for clarity, can be formed into the tank shown in Fig. 1 by procedure consisting of building the inner lining of the tank on a suitable form. 'I'his inner lining is heated to polymerize the seaming cement after which the other laminae are applied and cementtank emed in designated succession.

amides and interpolyamides obtained from the previously mentioned polyamide-forming reactants only. The relatively thick, rubbery, solvent resistant layer indicated at 9 in the drawing can, however, be composed of the rubbery polymers, examples of which are the superpolyester-amides such as the reaction product of hexamethylenediammonium adipate, adipic acid and ethylene glycol, or of other polyamide-forming compositions containing glycols, hydroxy acids, amino a1- cohols, etc.

A polyamide which is of outstanding value as the inner liner of the fuel cells of this invention because of its high impermeability in thin films to the fuel together with the ease in obtaining these lms from solution is the interpolyamide obtained from substantially equimolecular amounts of hexamethylenediamine, adipic acid, sebacic acid and aminocaproic acid, the proportions of these reactants preferably being such as would yield 40% of hexamethylene adipamide, 30% of hexamethylene sebacamide, and 30% of the aminocaproie acid polymer. This polyamide is most conveniently made by heating to polymerization a mixture of the diamine-dibasic acid salts (e. g. hexamethylenediammonium adipate and hexamethylenediammonium sebacate) with the selfpolymerizable amino acid. This polyamide is readily soluble in suitable and available solvents, such as ethanol-water mixtures, hot alcohols such as butanol, and chlorinated hydrocarbon-alcohol mixtures. In the case of this polyamide, as in the case of other polyamides yielding thin-imperme able lms presenting difficulty from the standpoint of adhesion, it is preferred to use as the adhesive certain resins obtained by reacting formaldehyde with other resin-forming reactants, namely, phenol-formaldehyde resins as exemplied by the reaction product of diphenylol-propane and formaldehyde, and 'sulfonamide-formaldehyde resins as exemplified by the reaction product of toluenesulfonamides and formaldehyde.

The thin polyamide film for example, is attached to the solvent resistant synthetic rubber layer 9 by means of an anchor coat composed of equal parts of a solution of diphenylol-propaneformaldehyde resin in one part of ethyl alcohol and of a solution of one part the above described interpolyamide in a mixture of' one-half part ethyl alcohol and one-half part water. This coating is applied to the base surface 9 after which the polyamide is applied from a film-forming solution which can be the solution of the polyamide in the alcohol and water mixture mentioned above. The polyamide is thus applied in a series of successive coatings until a nlm which is preferably from .3 mm. or approximately 12 mils (0.6 oz./sq. yd. by weight) to .05 mm. or approximately 2 mils (l oz./sq. yd. by weight) is built up. The adhesive can be applied alone from a solution of the resin in organic solvent instead of as a co-solution with the polyamide. For production coating of the resin and polyamide on rolls of the base material comprising the layer 9 or this layer attached to the other layers, application of the solution by regular knife coating is preferred, although the surface coatings can be applied by roller coating, hand brushI or spray gun methods.

Phenol-formaldehyde and sulfonamide-formaldehyde resins in addition to those mentioned above which can be used in bonding the thin polyamide lm to the synthetic rubber layer include modified phenol-formaldehyde resins known under the trade names of BU 1680 and HHI Amberol, and Santolite resins designated as MS and MHP.

Other polyamides which yield from solution thin, flexible, fuel-impermeable films and which can be bonded to the synthetic rubber layer by the above mentioned resins include the polymers obtained from hexamethylenediammonium adipate and decamethylenediammonium sebacate; hexamethylenediammonium adipate and aminocaproic acid or epsilon-caprolactam; hexamethylenediammonium adipate, hexamethylenediam.. monium azelate, and aminocaproic acid; hexamethylenediammonium adipate and 12-aminostearic acid; hexamethylendiammonium adipate, hexamethylenediammonium sebacate and piperazinium adipate.

The synthetic rubbers referred to herein which are resistant to petroleum and other hydrocarbon solvents are materials of the kind which have been previously used in the manufacture of flexible fuel containers. These rubbers, which are defined in Bureau of Standards Circular C-427, last paragraph on page 3, include ethylene polysulfide rubbers known as Thiokol, and those derived from butadiene, known under the trade names of Perbunan, Hycar, Ameripol, Chemigum and Neoprene Type I which is formed by the polymerization of 2-chlorobutadiene.

The transpiration rate of fuels through the inner liner of the improved fuel cells described herein is much less than in the case of the fuel tanks of like type heretofore used. Thus with an inner liner of the polyamide previously mentioned prepared from hexamethylenediammonium adipate, hexamethylenediammonium sebacate, and aminocaproic acid, the transpiration rate, depending on the particular conditions, is from one-fth to one-tenth that of the inner liner of the previously known cells.

The self-sealing cells disclosed herein are, for the reasons pointed out above, of unusual value for use as the fuel tanks of vehicles subjected to gun fire. The present flexible fuel `containers are highly resistant to the leaks caused by Vibration which often occur from this cause in metal tanks. The insertion of the present flexible selfsealing cells in a metal container is, however, not precluded, although this practice is not usual. This invention also makes possible the manufacture of improved iiexible fuel tanks of the nonsealing type. Such tanks may, for example, be constructed from a fabric coated on one or both sides with neoprene or other synthetic rubber which bears a skin coating of a polyamide as inner liner in contact with the fuel, or they may be constructed from an unsupported sheet of neoprene or other synthetic rubber having an inner skin coating of polyamide and without fabric backing. Such cells are usually supported in a metal container since their cell walls have little mechanical strength. The improved fuel tank of this invention is advantageously used for all purposes to which non-rigid synthetic rubber fuel storage tanks are put, for example in airplanes, trucks, military tanks and boats.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that I do not limit myself to the specic embodiments thereof except as de- Ifined in the appended claims.

I claim:

l. A self-sealing fuel container, the walls of which comprise flexible sheet material comprising a plurality of adherent laminae, said laminae comprising an outer layer of raw rubber adapted to swell on Contact with a hydrocarbon liquid, a .layer which mechanically expands to close openings caused by perforations and which comprises plasticized neoprene, a layer f neoprene which is substantially harder than said last mentioned layer and which has substantial resistance to the solvent action of hydrocarbon liquid, and a layer of polyamide which is suiciently thin to retain the flexibility of said sheet material but which is essentially impermeable to hydrocarbon liquids, said polyamide layer being a film composed of superposed polyamide coatings consisting essentially of amide-forming reactants and having a total thickness of from .05 mm. to .3 mm.

2. A self-sealing fuel container, the Walls of which comprise flexible sheet material comprising a plurality of adherent laminae, said laminas` comprising an outer layer of raw rubber adapted to swell on contact with a hydrocarbon liquid, a layer which mechanically expands to close openings caused by perforations and which comprises plasticized neoprene, a layer of neoprene which is substantially harder than said last mentioned layer and which has substantial resistance to the solvent action of hydrocarbon liquid, a lm of resin selected from the group consisting of phenolformaldehyde and phenolsulfonamide resins, and a polyamide layer which is bonded by said resin to said harder neoprene layer and which is sufliciently thin to retain the flexibility of said sheet material but which is essentially impermeable to hydrocarbon liquids, said polyamide layer being a film composed of superposed polyamide coatings consisting essentially of amide-forming reactants and having a total thickness of from y.05 mm. to .3 mm.

3. The self-sealing fuel container set forth in claim l in which said resin is the reaction product of diphenylolpropane and formaldehyde.

4. The fuel container set forth in claim 1 in which said polyamide is the interpolyamide obtained from substantially equimolecular amounts of hexamethylene diamine, adipic acid, sebacic acid, and aminocaproic acid.

DAVID J. SULLIVAN. 

